1. Field of the Invention
The present invention relates to methods and systems for treating blood vessels. More particularly, the invention relates to methods and systems for treating vascular malformations, such as aneurysms. Even more particularly, the present invention relates to methods and systems for treating an aneurysm with a microcatheter and an embolic agent.
2. State of the Art
An aneurysm is a localized, blood-filled balloon-like bulge in the wall of a blood vessel. Aneurysms can commonly occur in arteries at the base of the brain, i.e., at the circle of Willis. Another common type of aneurysm is an aortic aneurysm in the main artery carrying blood from the left ventricle of the heart.
The development of an aneurysm causes a turbulent blood flow within the vessel localized at bulge which in turn increases wall stress at bulge and consequent increased dilation. In hemodynamic terms, the coupling of aneurysmal dilatation and increased wall stress is approximated by the Law of Laplace. The Law of Laplace applied to a cylinder states that the (arterial) wall tension is equal to the pressure times the radius of the arterial conduit (T=P×R). As diameter increases, wall tension increases, which contributes to more increase in diameter. When the size of an aneurysm increases, there is a significant risk of rupture, resulting in severe hemorrhage, other complications or death. Eventually all aneurysms will, if left to complete their evolution, rupture without intervention. Current treatments seek to fill the aneurism to thereby reduce the wall stress at the aneurysm in response to the stress induced as the blood flows through the vessel.
In one method, a microcatheter is advanced directly into the aneurysm, and embolic beads or other embolic agents are infused directly into the aneurysm. However, infusion with a standard microcatheter routinely leads to non-targeted delivery of the embolic agent, either downstream (antegrade) or backwards (reflux), which can lead to mild to severe complications.
Another method of treatment includes placing a stent in the blood vessel across the aneurysm. Once the vessel is stented, a catheter is advanced through the stent and laterally into the aneurysm. With the catheter in position, endovascular coils are advanced from the catheter and into the aneurysm until no additional coils can be placed; i.e., the aneurysm is completely occluded with the coils flush with the vessel wall and outer surface of the stent. The coils initiate a clotting or thrombotic reaction within the aneurysm that, when successful, eliminates the aneurysm. An advantage of this method is that it can be performed without occluding the blood vessel to blood flow. The stent separates the occlusion zone from the blood flow within the vessel and blood flow is maintained while the coils are advanced into the aneurism. However, the method is only suitable for use on larger vessels that can accommodate being stented. In addition, the method requires that the stent remain implanted permanently. It is generally undesirable to have a permanent implant where an option exists for treatment without an implant.
It is also known to treat an aneurysm by filling the aneurysm with a slow setting liquid embolic agent such as ethylene vinyl alcohol copolymer dissolved in the organic solvent dimethyl sulfoxide (DMSO). Such an liquid embolic agent is available from EV3 of Irvine, Calif. under the brand ONYX™. Such current method includes positioning a PTFE balloon within the blood vessel so that it extends across the aneurysm. A microcatheter is also positioned within the blood vessel and enters the aneurysm. Such microcatheter may extend alongside the balloon or be partly carried by the balloon. The balloon is inflated to segregate the aneurysm from the blood vessel, and the liquid embolic agent is injected through the microcatheter into the aneurysm. As the aneurysm is filled with the embolic agent, the balloon keeps the embolic agent within the aneurysm. The microcatheter is withdrawn once the aneurysm is filled. Once the embolic agent cures, the balloon is removed. The balloon defines a very smooth repair to the vessel wall. A successful treatment operates to reduce the wall stress at the aneurism. However, because the balloon completely occludes blood flow during the treatment and the liquid agent requires a significant amount of time to set as a solid, there is the opportunity for inducing a local ischemic event due to a lack of blood supply during the treatment time.